The present invention relates to a test slider for testing the smoothness of a disc in a disc drive system, and more particularly relates to an integrated piezoelectric and magnetoresistive (MR) thermal asperity transducer slider to concurrently detect defects in a magnetic disc.
In order to certify that a magnetic disc is adequately smooth for use in a disc drive system, tests must be performed on the disc. One type of testing is performed by utilizing a test slider having a piezoelectric element bonded thereon. When any part of the slider contacts a protrusion on the surface of the disc, the slider will vibrate from the impact. The piezoelectric element bonded on the slider senses these vibration forces acting on the slider, exhibiting a voltage between its terminals representative of the forces experienced by the element. If the vibration force sensed by the piezoelectric element exceeds a predetermined design level, or if vibration occurrences exceed a predetermined design frequency, then the disc media under test is not adequately smooth to be used in applications.
There are several problems involved with utilizing piezoelectric test sliders to test the smoothness of a disc. By bonding the piezoelectric element to the slider, the piezoelectric element loses some of its sensitivity to forces acting on the slider, since some of these forces may be absorbed through the bond to the piezoelectric element. Piezoelectric test sliders are therefore relatively insensitive to narrow defects and asperities in the disc being tested. In addition, the process of bonding a piezoelectric element to the slider affects the aerodynamic characteristics of the slider, which are desirably tightly controlled. Finally, the process of assembling a piezoelectric element on a slider is a tedious and expensive undertaking, and is not standard since piezoelectric elements are not employed on actual read/write heads. Changes in the process of manufacturing the slider must be made, which makes manufacturing test sliders less efficient.
Another type of testing is performed by equipping a test slider with thermal asperity sensor, such as a MR transducer. A thermal change occurs in the sensor upon detecting a defect or asperity in the disc at the transducer, which changes the resistance of the MR element and thereby indicates the presence of a defect on the disc. The defect or asperity may be a depression or a rise (bump) in the disc surface, as each affects the resistance characteristics of the MR element oppositely. However, if the transducer (which is positioned on a rail at the trailing edge of the slider) does not directly confront the defect on the disc, the MR sensor is unable to detect the presence of the defect. Thus, for wide defects, the slider may "bounce" over the defect after contacting it near the leading edge of the slider, the force of which would affect the height of the thermal asperity sensor over the surface of the disc and thereby cause errors in detecting the defect.
One solution to the problems presented in testing the smoothness of a disc has been to perform two separate glide tests, one with a piezoelectric test slider and one with a separate thermal asperity test slider. The piezoelectric slider is used for best performance in detecting "short and fat" defects on the disc, while the thermal asperity slider is used for best performance in detecting "tall and thin" defects in the disc.
However, additional problems are presented by using separate piezoelectric test sliders and thermal asperity test sliders. Greater time and effort is involved in performing two separate tests. Also, the potential for inaccuracies in measurements is present, since the piezoelectric test slider may not have identical flying characteristics as the MR test slider.
There is a need in the art for an integrated thermal asperity and piezoelectric sensing device to allow testing of disc smoothness with a single test slider that is simply designed and provides reliable measurements.